Basically, if I can tell the author just slapped certain portions together out of habit or necessity, and didn't put enough thought into it. Like, an uninspired backstory, or or a boring effect, bad proofreading, just a myriad of things that can be chalked up to laziness or haste to post.

Agh, forgot that one. When appropriate, that doesn't bug me, but when people write sentences like "Subject is a giant monkey with…" or "Subject took seven dollars from my wallet and proceeded to…" or shit like that. Note how it is not "The subject is" but "Subject is" that bugs the crap out of me.

SCP-XXXX is to be stored in a box in a random containment cell. This cell is to be locked by a triple-extra-safe combination lock with internal and external non-euclidian tumbler-pistons obfuscated according to the Fdtn:Lck-A:Weeblefuck protocol. The lock is to be checked for non-conformity twice daily, with the combination shifted every three hours using a combination of SHA-1 and whirlpool hashing methods. The lock is to verified SecDamnLock compatible with at least three seals of LockPr0n merit having been issued by the [REDACTED] Foundation.

I will not downvote just for one of those, even for several of those, but they annoy me, greatly (with the annoyance roughly decreasing towards the bottom of the list), and I will probably enjoy an article less if it has them.

Redaction in the containment procedures
List redaction "I ate a hamburger, fries, and [DATA EXPUNGED]."
Vital information being redacted.
A list of addendum/experiments/incidents where one is redacted with no context. (Addendum XXXX-3 [DATA EXPUNGED])
Poorly written interview logs.
Use of the word "memetic" as a synonym for "psychic"
Things that make you forget about things, which we know happens because it was written in the logs.

There are no mimes here, only obsessive spelling faeries. ~Pig_catapult